An event delivery system that, upon occurrence of a state change in a given observation target, computerizes the state change and notifies the state change to recipients who desire for the delivery of the information is known (refer to Non-Patent Literature 1, for example). FIG. 1 is an example of a related event delivery system. The event delivery system of FIG. 1 is composed of publisher nodes (P1, P2), broker nodes (B1 to B5), a rendezvous node R at the top of an event delivery tree, and subscriber nodes (S1, S2). The event delivery system of FIG. 1 operates as follows.
The publisher node P1 that intends to issue an event first advertises the event. As shown in FIG. 1, the advertisement processing is executed by transmitting advertisement information a1 from the publisher node P1 to the rendezvous node R. The broker node B1 creates a routing table for advertisement when it receives the advertisement information a1 from the publisher node P1. Specifically, it creates setting of:
Transmission source (Publisher node P1)-Transfer destination (Rendezvous node R).
The route Rt1 of the event delivery path which is created at this point:
(Publisher node P1)-(Broker node B1)-(Rendezvous node R)
is used when the publisher node P1 issues event information p1.
The publisher node P2 that intends to issue an event also performs the same processing, that is, advertises advertisement information a2 to the rendezvous node R. The transmission of the advertisement information a2 to the rendezvous node R is terminated at the broker node B2. This occurs when the same type of event is advertised, for example, in the case where the advertisement information a1 and the advertisement information a2 are in an inclusive relation. In FIG. 1, because the advertisement information a1 has already advertised the delivery route of:
(Broker node B1)-(Rendezvous node R),
the delivery route set for the advertisement information a1 is used as the delivery route from the broker node B1 to the rendezvous node R for the advertisement information a2.
On the other hand, the subscriber node S1 that intends to receive the advertised event transmits request information s1 for receiving the event to the rendezvous node R. The request information s1 reaches the rendezvous node R through the route Rt2:
(Subscriber node S1)-(Broker node B3)-(Broker node B1).
in FIG. 1. Further, the request information s1 is transferred also to the broker node B2. This occurs when conditions for the advertisement information a2 that intends to advertise the event information p1 and the request information s1 that intends to receive the event information p1 match. To be more specific, the broker node B3 and the broker node B1 on the path through which the request information s1 is transferred refer to the routing table that is constructed at the time of transferring the advertisement information a1 to the rendezvous node R. In this reference, if conditions for the event to be advertised and the event to be received match, the request information s1 is transferred in the reverse direction through the route constructed for the advertisement information a1. Specifically, in FIG. 1, the request information s1 is transferred from the broker node B1 to the broker node B2. Although not shown in FIG. 1, the event that is advertised by the advertisement information a2 based on this processing is delivered as event information p2 through the delivery route of:
(Publisher node P1)-(Broker node B2)-(Broker node B1)-(Broker node B3)-(Subscriber node S1)
when a state change occurs in the publisher node P2.